Pollution-free well cuttings disposal apparatus

ABSTRACT

Apparatus for cleaning oily mud from cuttings at offshore drilling locations and disposing of the cuttings without the formation of an oil slick comprising a cuttings washer in which the cuttings are sprayed with a wash liquid and then conveyed to a partially submerged down pipe and discharged therein below the water level, whereby the cuttings fall to bottom, releasing their oily coating which rises within the down pipe to a submersible pump therein which pumps the released oil to a receiver for optional recycling into the mud system.

United States Patent 11 1 Stearns et al.

1451 Aug. 26, 1975 [54] POLLUTION-FREE WELL CUTTINGS 3,563,255 2/1971Morris 134/133 DISPOSAL APPARATUS 3,688,781 9/1972 Talley, Jr... 134/110X 3,765,430 10/1973 Muller 134/109 [75] Inventors: Marvin O. Stearns,London,

England; James Houston Primary Examiner-Robert L. Bleut ge Attorney,Agent, or Firm-Delmar H. Larsen; Roy F. [73] Assignee: NL Industries,Inc., New York, NY. House; Robert L. Lehman [22] Filed: I Oct. 5, 197357 ABSTRACT [21] Appl. No.: 403,999 1 Apparatus for cleaning oily mudfrom cuttings at offshore drilling locations and disposing of thecuttings [52] 1 2 851 5 9 gig/ 2 12 without the formation of an oilslick comprising a cuttings washer in which the cuttings are sprayedwith a II}!- wash and h conveyed to a partially Flld of Search merged dand discharged therein below the 175/88 208; 209/159; 210/216 waterlevel, whereby the cuttings fall to bottom, re-

leasing their oily coating which rises within the down [56] Referencescued pipe to a submersible pump therein which pumps the UNITED STATESPATE T released oil to a receiver for optional recycling into 2,576,28311/1951 Chaney 175/208 X e d system. 2,950,724 8/1960 Roederer, Jr.134/183 3,378,018 4/1968 Lawter 134 109 5 Clams 4 Drawmg Flgul'es /4 /5Z3 TI /0 POLLUTION-FREE WELL currmos DISPOSAL I APPARATUS This inventionrelates to the art of rotary well drilling in offshore locations usingoily drilling fluids, and more particularly to an apparatus and processwhich permits the economical disposal of cuttings without polluting thebody of water where the drilling takes place.

As is well known, the increasing worldwide demand for petroleum has ledto increased drilling in offshore locations, such as the Gulf Coast ofthe United States, the Pacific Coast, the North Sea, and elsewhere. Suchdrilling is carried out by the rotary process, in which cuttingsdislodged by the bit are raised to the surface by means of a drillingfluid or a mud, which fills the bore hole and is circulated continuouslyduring drilling, being pumped downwardly inside the drill string to thebit and thence upwardly in the annular space between the drill pipe andthe walls of the bore hole. At the surface, the mud is freed of cuttingsby mechanical means and is then recirculated down the hole through thehollow drill pipe as before.

In many locations, it is preferred and may even be indispensable toutilize a drilling fluid having oil as its continuous phase. Such afluid is commonly known as an oil base or oil emulsion mud. When this isthe case, it will be readily appreciated that the cuttings brought tothe surface will be coated with a film of oil. Simply disposing of thecuttings by dumping them overboard results in at least a portion of theoil film eventually coming to the surface of the body of water as an oilslick, which is an intolerable situation and indeed is prohibited bylaws and regulations in most countries of the world. Since the cuttingsare of substantial total volume, disposal by transporting them to landis not only expensive, but is not always a complete solution regardlessof expense because oil soaked cuttings may not be indiscriminatelydumped at any randomly selected onshore location. A pressing needtherefore exists for a mechanically reliable, relatively simple, andrelatively economical arrangement for processing such cuttings at theoffshore drilling location in such a manner that they can be readilydisposed of without causing the formation of an oil slick.

principal components of the apparatus in an offshore drillinginstallation.

FIG. 3 is a plan view of the cuttings separation and washing portions ofour inventive apparatus.

FIG. 4 is an elevation partly in section of the cuttings .washer shownin FIG. 3.

' Generally speaking, and in accordance with an illustrative embodimentof our invention, at an offshore drilling location we provide apartially submerged down pipe extending both above the surface of the'water and below the surface of the water; a cuttings spraying devicereceiving cuttings which have been separated from the drilling mud,spraying them with a cleaning liquid and discharging them into a flumewhich conveys them to the down pipe and discharges them interiorly ofthe down pipe and below the surface of the water; means for collectingthe wash or cleaning liquid when located with silt and for pumping itinto a desilting means such as a cyclone and returning the desiltedliquid to the cuttings washer; a submersible pump within the down pipeand at the water level therein or adjacent said water level which servesto pump oil released from the cuttings and which has risen to the levelof the top of the liquid in the down pipe; an oil-water separatorreceiving the mixture of oil and water pumped out by the pump fromwithin the down pipe; and a discharge receiver for the oil emerging fromthe oil-water separator.

The arrangement and function of our inventive apparatus will be morereadily understood by reference to the drawings.

In FIG. 2, 10 indicates a portion of the platform of an offshoredrilling location, which is supported by a number of vertical supportsof which one, 11, is indicated in the figure. 12 indicates the downpipe, which is conveniently welded or otherwise attached to the supportleg 11. The down pipe is conveniently of 20-inch diameter steel pipe andshould extend about 30 feet below the normal water level, provided ofcourse that the water depth at the drilling locality permits this.Otherwise, it should extend to within not closer than about 10 feet ofthe ocean or lake bottom. The down pipe 12 should also extendsufficiently above the normal water level so as to be above the waterregardless of tidal and normal wave action, for which 8 or 10 feetnormally suffices. Of course, in estuarine and like locations wherelarge tidal action occurs suitable allowance should be made therefor.The encased drilling string 13 is shown diagrammatically, with the flowline 14 indicating the conduit in which the drilling fluid with itsburden of cuttings is conducted to vibrating screens 15 and 16, whichshakes a substantial portion of the oily mud from the cuttings, fromwhich the cuttings are discharged into a cuttings Washer 17, whichconveniently takes the form of a relatively small vibrating screen 18over the top of which is arranged a series of spray nozzles 19, 20, 21,etc., supplied with wash liquid from a header 22, also shown in FIG. 4.The cuttings are thus washed with the wash liquid, a large proportion ofwhich falls through the screen carrying with it a portion of the oilymud from the cuttings. However, even with the spray action and vibratoryscreen action to which the cuttings are subjected in the cuttings washer17, not all of the oily drilling fluid is necessarily removed from thecuttings. In any case, some of the wash liquid, to be described indetail hereinbelow, amalgamates with the residual oil on the cuttingsand renders it more readily susceptible to eventual dislodgement whenimmersed in the water, generally sea water, in the down pipe 12. Thecuttings are simultaneously washed and propelled to the discharge end 23of the cuttings washer, whence they fall into flume 24 and are conveyedby the action of gravity into the down pipe 12. Water from the body ofwater surrounding the platform 10 or from the separator 29 may be pumpedto the flume 24 to assist in conveying the washed cuttings to thedown-pipe 12. The flume 24 terminates and discharges the cuttings belowthe water level and below the pickup level of the submersible pump 25,as may be seen from FIG. 2. The cuttings fall through thedown pipe 12,and eventually accumulate on the sea bed or'lake bed 26 as a tailingspile 27. In their passage through the down pipe 12, however, and in viewof the fact that the cuttings are essentially water wettable, and moreparticularly aided by the amalgamated wash liquid carried by thecuttings, the oil together with wash liquid is displaced from thecuttings by the water and rises upwardly within the down pipe 12 to forman oil layer adjacent to the pump 25. The latter pumps the top layer ofliquid within the down pipe, which as a practical matter includes bothoil and water, and pumps it through conduit 28 to the oil waterseparator 29. The oil freed of any water is then pumped from theseparator 29 through conduit 30 to the oil receiving tank 31.

In some cases silt is produced by the washing action in washer 17. Inthat event, we prefer to collect the wash liquid at the bottom of 17through exit pipe 35, pump it by means of pump 32 to a desilting cyclone33 and back to header 22, the silt solids being discharged from thecyclone at 34. Cyclones are well-known in the art. See, for example, thebook Cyclones in Industry, K. Rietema et al., Ed., Elsevier, Amsterdamand New York, 1961.

As suggested earlier, since the oil removed from the cuttings wasderived from drilling fluid in the first instance, and since the washfluid is compatible with the drilling fluid, it is convenient andpractical to utilize the oil accumulating in the oil receiving tank 31for the oil make-up requirements of the drilling fluid.

FIG. 1 shows a flow diagram of the cuttings washing and disposal system,in which the contaminated cuttings as discharged from screens 15 and 16are fed to the cuttings washer 17 where they are sprayed with washliquid through header 22 and thence conveyed through flume 24 into downpipe 12 which functions as a liquid-solid separator, from which thediscarded solids accumulate on the sea bed and the oil with some waterfrom down pipe or separator 12 is pumped to the oil-water separator 29,from which the water is discarded and oil is returned eventually to thewell fluid. FIG. 1 also shows the optional desilting means 33 and pump32, as already described.

The vibrating screens 15 and 16 as well as the vibrating screen portion18 of the cuttings washer 17 are conventional vibrating screens, typicalexamples of which may be seen in the book by A. M. Gaudin entitledPrinciples of Mineral Dressing, McGraw-Hill, New York 1939, pages157l61. The oil-water separator 29 is of the common industrial typefrequently used in oil field practice.

Coming now to the wash liquid, this should comprise at least about 10%by volume of an organic solvent which is miscible with crude oil andalso has substantial water solubility. While low boiling solvents suchas acetone, methyl-ethyl ketone and dioxane meet these requirements,they are less desireable than higher boiling solvents because of thefire hazard associated with their high volatility. A large number ofsuitable solvents having the properties just mentioned are commerciallyavailable at reasonable cost. We prefer such higher boiling mutualsolvents for oil and water as ethylene glycol monoisobutyl ether,commercially available under the registered trademark of IsobutylCellosolve. Other mutual solvents which are suitable include diethyleneglycol monobutyl acetate, ethylene glycol ether, ethylene glycolmonomethyl ether acetate, diethylene glycol diethyl ether, anddiethylene glycol mono-nhexyl ether. These form the subject matter of apatent application of Thomas C. Mondshine assigned to the assignee ofthe instant application, and filed concurrently with this application,and entitled Laundering of Oil Base Mud Cuttings.

The wash liquid, as mentioned, should include at least 10% by volume ofthe mutual solvent for petroleum oil and water such as has beendescribed, and may comprise as much as 100% of such a solvent or amixture of several such solvents. However, we find that results arealmost equally good by using as little as 10% of the mutual solvent in acarrier of petroleum oil, preferably diesel oil. By the term mutualsolvent, specific examples of which have been given, we mean an organicsolvent having substantial solubility in both petroleum oil, such asdiesel oil, and water.

In a field trial of our inventive system, an offshore ocean drillinglocality was equipped with the apparatus shown and described herein.Drilling was carried out commencing at a depth of 10,500 feet using anoil-base mud having a continuous phase of from about to by volume of oiland a dispersed phase of from about 20 to 25% by volume of watercontaining from 30 to 40% by weight of calcium chloride. The vibratingscreen portion of the cuttings washer was about 2 feet wide by 6 feetlong, with a l00-mesh screen. The cuttings took about 1 minute totraverse the screen during which time they were sprayed with a mixtureof 4 parts by volume of diesel oil and 1 part by volume of IsobutylCellosolve. The installation operated to a high degree of satisfactionand the cuttings drilled up in the interval drilled with the oil basemud were discharged to the sea bottom with no production of an oil slickat the surface.

We wish it to be understood that we do not desire to be limited to theexact details of construction and operation shown and described, forobvious modifications will occur to a person skilled in the art.

Having described the invention, we claim:

1. Apparatus for removing oil from drill cuttings at an offshoredrilling location above the surface of a body of water comprising incombination a platform; a partially submerged down pipe extending bothabove the surface of the water and below the surface of the water; meanson said platform for shaking oily mud from said cuttings by vibratoryscreening action; means on said platform for discharging said shakencuttings onto cuttings washer means; means on said platform andassociated with said cuttings washer means for spraying said cuttingswith a wash liquid; pump means on said platform for collecting said washliquid subsequent to its contact with said cuttings and for pumping itto desilting means located on said platform; return flow means forrecirculating said desilted wash liquid to said cuttings washer means;means for conveying said washed cuttings from said platform to a pointwithin said down pipe and below the surface of said water; pump meansfor pumping oil dislodged from said cuttings in said down pipe andpresent within said down pipe adjacent the surface level of said waterto oil-water separating means; means for receiving oil discharged fromsaid oilwater separating means.

2. Apparatus in accordance with claim 1 wherein said detergent washliquid comprises at least 10% of its volume of a mutual solvent forpetroleum oil and water.

3. Apparatus in accordance with claim 1 wherein said desilting meanscomprises a cyclone.

4. Apparatus in accordance with claim 3 wherein said detergent washliquid comprises at least 10% of its volume of a mutual solvent forpetroleum oil and water.

5. Apparatus for removing oil from drill cuttings at an offshoredrilling location above the surface of a body of water comprising incombination a platform; a par tially submerged down pipe extending bothabove the surface of the water and below the surface of the water; meanson said platform for shaking oily mud from said cuttings by vibratoryscreening action; means on said platform for discharging said shakencuttings onb cuttings washer means located on said platform; meanslocated on said platform associated with said cuttings washer means forspraying said cuttings. with a wash liqcharged from said oil-waterseparating means.

1. Apparatus for removing oil from drill cuttings at an offshoredrilling location above the surface of a body of water comprising incombination a platform; a partially submerged down pipe extending bothabove the surface of the water and below the surface of the water; meanson said platform for shaking oily mud from said cuttings by vibratoryscreening action; means on said platform for discharging said shakencuttings onto cuttings washer means; means on said platform andassociated with said cuttings washer means for spraying said cuttingswith a wash liquid; pump means on said platform for collecting said washliquid subsequent to its contact with said cuttings and for pumping itto desilting means located on said platform; return flow means forrecirculating said desilted wash liquid to said cuttings washer means;means for conveying said washed cuttings from said platform to a pointwithin said down pipe and below the surface of said water; pump meansfor pumping oil dislodged from said cuttings in said down pipe andpresent within said down pipe adjacent the surface level of said waterto oil-water separating means; means for receiving oil discharged fromsaid oil-water separating means.
 2. Apparatus in accordance with claim 1wherein said detergent wash liquid comprises at least 10% of its volumeof a mutual solvent for petroleum oil and water.
 3. Apparatus inaccordance with claim 1 wherein said desilting means comprises acyclone.
 4. Apparatus in accordance with claim 3 wherein said detergentwash liquid comprises at least 10% of its volume of a mutual solvent forpetroleum oil and water.
 5. Apparatus for removing oil from drillcuttings at an offshore drilling location above the surface of a body ofwater comprising in combination a platform; a partially submerged downpipe extending both above the surface of the water and below the surfaceof the water; means on said platform for shaking oily mud from saidcuttings by vibratory screening action; means on said platform fordischarging said shaken cuttings onto cuttings washer means located onsaid platform; means located on said platform associated with saidcuttings Washer means for spraying said cuttings with a wash liquidwhich comprises at least 10% of its volume of a mutual solvent forpetroleum oil and water; means for conveying said washed cuttings fromsaid platform to a point within said down pipe and below the surface ofsaid water pump means for pumping oil dislodged from said cuttings insaid down pipe and present within said down pipe adjacent the surfacelevel of said water to oil-water separating means; means for receivingoil discharged from said oil-water separating means.